Gas liquefier



June 20, 1967 u T. J. WEBSTER GAS LIQUEFIER Filed Oct. 2l, 1965 INVENTOR Toh BY m0@ lll- ATTORNEYS` United States Patent O 3,326,015 GAS LIQUEFIER Thomas .lohn Webster, Ashford, England, assignor to The British Oxygen Company Limited, a British company Filed (9ct. 21, 1965, Ser. No. 499,934 Claims priority, application Great Britain, July 7, 1965, 28,837/ 65 4 Claims. (Cl. 62-514) ABSTRACT F THE DISCLOSURE A gas liquefier having a coiled capillary tube positioned within a cavity of a dewar. Insulation material is positioned on the exterior of the coil to form a seal between the coil and the dewar. The apparatus employs the Joule-Thomson effect.

This invention relates to gas liquefiers in which s0- called permanent gas at high pressure is expanded to substantially atmospheric pressure in an expansion nozzle or orifice a ter passing through a heat exchange coil, the expanded gas flowing back over the coil in countercurrent with the incoming high pressure stream. These liquefiers will be referred to as liquefiers of the type described. Joule-Thomson expansion at the orifice produces cooling which, due to the heat exchanger, procee-ds progressively until a sufficient depth of temperature is reached to cause liquefaction of a portion of the gas issuing from the orifice. The so-called permanent gases which can be liquefied in this manner include air, oxygen, nitrogen, argon, krypton, and xenon.

Hydrogen can also be liquefied in this manner but the compressed stream of hydrogen must be pre-cooled with a liquefied gas such as nitrogen before it is fed into the heat exchanger.

The heat exchanger in such liquefiers may take the form of a coil, a coiled helix or a series of coils or coiled helices wound round a mandrel which is inserted in a vacuum insulated cylindrical flask or dewar. The inner wall of the dewar in combination with the mandrel serves to provide an annular passage for the return gas, causing it to traverse the coil.

Such liquefiers are primarily designed to meet sporadic demands for the production of small quantities of liquefied gas from high pressure gas stored in a cylinder. A typical instance of such a deman-d is for demonstration purposes in educational establishments. In such cases the dewar is made of transparent material such as glass so that the formation of liquid can be easily seen. Another example is the cooling of an instrument, such as an infra red detector, which can conveniently be housed in the transparent vessel. Other sporadic demands for small quantities of liquefied gas arise in cryosurgery and in the low temperature preservation of biological tissue, such as corneal graft material.

Where the demand for small quantities of liquefied gas is sporadic, storage of the gas in the liquid state is uneconornical due to evaporation losses. The provision of a compressor to provide a source of high pressure gas, such as air, for liquefaction entails substantial capital outlay not only in respect of the compressor but also for the purification train which is essential to prevent solid particles of high melting point constituents, such as Water and carbon dioxide, from blocking the heat exchanger passages.

Gas to be liquefied in liquefers of the type described is, therefore, generally obtained from storage vessels or cylinders containing the gas at pressures of 2,000 p.s.i. and higher. The process of liquefaction cannot be sustained Patented June 20, 1967 nce once the pressure has fallen below about 800 p.s.i. and hitherto with liquefiers of known type, it has not been possible to achieve liquefaction from a warm start up if the initial pressure in the cylinder is much below 2,000 p.s.1.

It is an object of this invention to provide a liquefier of the type described in which the onset of liquefaction from a warm start up is achieved with lower gas consumption than heretofore.

Another object of this invention is to provide a liquefier by means of which a liquefied fraction can be obtained from a warm start up using a source of pressure lower than 2,000 p.s.i.

According to this invention there is provided a gas liqueer of the type described comprising a substantially cylindrical heat insulated vessel, a substantially cylindrical heat exchanger formed from capillary tubing, and lfitting into said vessel, said heat exchanger having an expansion orifice at one end, an inlet header connected to the other end of said heat exchanger for coupling the heat exchanger to a source of compressed gas, a sheath of heat insulating material `fitting round the heat exchanger to inhibit thermal interchange between the heat exchanger and the vessel, and sealing means to secure the heat exchanger in the vessel and to direct the return liow of expanded gas inside the sheath in thermal contact with the capillary tubing.

The sealing means may conveniently be an integral part of the sheath.

The sheath is preferably wrapped tape of low heat capacity insulating material such as Terylene, fibre glass or aluminised Terylene.

The sealing means in such case can be formed from additional winding of tape about the inlet end of the heat exchanger to provide a seal at the mouth of the vessel.

The gas liquefier may be adapted to be fitted within a back-flush unit for the clearance of any blockage occurring in the capillary tubing.

An embodiment of the invention is shown by Way of example in the accompanying drawing which is a view in longitudinal section of a gas liquefier fitted into a dewar flask.

Referring to the drawing the liquefier comprises a double heat exchange coil 10 of coiled capillary tubing 11 wound around a mandrel 12. The mandrel 12 is a thin walled stainless steel tube three inches long, one end of which is soldered onto a central boss of a header 13. The mandrel tube is closed at its other end by a plug 14.

The double coil 10 is formed from a single l0 ft. length of capillary tubing 11 of 0.3 mm. inside diameter. This is first coiled into a Ihelix leaving its ends uncoiled, and is then straightened in the region of its centre 15 and bent into a U shape, the two arms of which are coiled around the mandrel 12 as a double helix. The uncoiled ends of the capillary tu-be extend into the header 13 and are scale-d thereto by soft solder, and within the header the open ends of the tube are bent over as indicated to minimize entry into the tubes of solid particles entrained in the gas stream. The header 13 is internally screwthreaded for the reception of an adaptor 16 having a nipple 17 for connection to a high pressure gas source such as a pressurized cylinder. The chamber Within the header is sealed by a resilient washer 18.

The central portion 15 of the tubing 11, which is located at the base of the U shape formed as described, is located in a small slot in the plug 14. In this region an orifice of about 0.003 inch diameter is drilled in the capillary tube wall, this providing an outlet orifice for presurized gas supplied to the tube ends via the header 13.

Alfter the coil has been formed, Terylene cord 20 is wrapped around the coil outside to -ll in the surface indentations and to give a relatively smooth cylindrical surface. Terylene tape is then tightly wound around the outside of the whole coil, so as to form an insulating sheath 21. An additional winding of tape 22 is provided around the inlet end ofthe coil so as to provide a plug which is a push lit into the dewar vessel 23. This plug provides sealing means which prevent return gas flow outside the sheath 21, so ensuring that all expanded gas passes over the coil. Apart from directing the return vgas in this way, the sheath reduces inflow of heat from the relatively warm inner wall of the dewar vessel, and substantially im- 4proves performance of the liquefier on Warm start-up.

It has been found that, in producing liquid air from compressed air at 2,000 p.s.i. the provision of the insulating sheath 21 reduces the time taken from Warm start-up to liquid production from 41/2 minutes to just over one minute. Furthermore, the minimum pressure needed to produce liquid with a warm start-up is reduced from 1,800 p.s.i; to 1,500 p.s.i. -by provision of the sheath.

With the liquefier described, at least three liquefactions from warm start-up can be demonstrated using the four litre cylinder containing dry air at 2,350 p.s.i. and producing liquid -for two minutes in each case. While warm start-up cannot be used with a starting pressure of less than 1,500 p.s.i. if the liquelier is operated continuously it can operate until the pressure drops to 800 p.s.i. or for about minutes starting at 2,350 p.s.i.

What is claimed is:

1. A lgas liqueer of the type described comprising a substantially cylindrical heat insulated vessel, a substantially cylindrical heat exchanger formed from capillary tubing, and fitting into said Vessel, said heat exchanger having an expansion orifice at .one end, an inlet header connected to the other end of said heat exchanger for coupling the heat exchanger to a source of compressed gas, -a sheath of heat insulating material fitting round the heat exchanger to inhibit Athermal interchange between the heat exchanger and the vessel, and sealing means to secure the heat exchanger in the vessel and to direct the return flow of expanded gas inside the sheath in thermal contact with the capillary tubing.

2. A gas liquefier of the type described comprising a substantially cylindrical he-at insulated vessel, a substantially cylindrical heat exchanger formed from capillary tubing, and fitting into said vessel, said heat exchanger having an expansion orifice at one end, an inlet header connected to the other end of said heat exchanger for coupling the heat exchanger to a source of compressed gas, a sheath of heat insulating material fitting round the heat exchanger to inhibit thermal interchange between theheat exchanger and the vessel, and sealing means which is an integral part of said sheath to secure t-he heat exchanger in the vessel Iand to direct the return flow of expanded gas inside the sheath in thermal contact with the capillary tubing.

3. A gas liquefier of the type described comprising a substantially cylindrical heat insulated vessel, a substantially cylindrical heat exchanger formed from capillary tubing, and fitting into said vessel, said heat exchanger having an expansion orifice at one end, an inlet header connected to the other end of said heat exchanger for coupling the heat exchanger to a source of compressed gas, a sheath consisting of Wrapped tape of low heat capacity insulating material fitting round the heat exchanger to inhibit thermal interchange be-tween the heat exchanger and the vessel, and sealing means to secure the heat exchanger in the vessel and to direct the return ow of expanded gas inside the sheath in thermal contact with the capillary tubing.

4. A gas liqueer of the type described comprising a substantially cylindrical heat insulated vessel, a substantially cylindrical Iheat exchanger formed from capillary tubing, and fitting into said vessel, said heat exchanger having an expansion orice at one end, an inlet header connected to the other end of said heat exchanger for coupling the heat exchanger to a source of compressed gas, a sheath consisting of wrapped tape -of low heat capacity insulat` ing material fitting round the heat exchanger to inhibit thermal interchange between the heat exchanger and the vessel, and sealing means consisting of anadditional winding of tape about said other end of the heat exchanger to secure the heat exchanger in the vessel and to direct the return ow of expanded gas inside the sheath in thermal contact with the capillary tubing.

References Cited UNITED STATES PATENTS 3,018,643 1/1962 Evers 62-514 X 3,021,683 2/1962 McInroy. 3,055,192 9/1962 Dennis 62-514 X 3,095,711 7/1963 Wurtz 62,-514

FOREIGN PATENTS 861,111 2/ 1961 Great Britain.

MEYER PERLIN, Primary Examiner. 

1. A GAS LIQUEFIER OF THE TYPE DESCRIBED COMPRISING A SUBSTANTIALLY CYLINDRICAL HEAT INSULATED VESSEL, A SUBSTANTIALLY CYLINDRICAL HEAT EXCHANGER FORMED FROM CAPILLARY TUBING, AND FITTING INTO SAID VESSEL, SAID HEAT EXCHANGER HAVING AN EXPANSION ORIFICE AT ONE END, AN INLET HEADER CONNECTED TO THE OTHER END OF SAID HEAT EXCHANGER FOR COUPLING THE HEAT EXCHANGER TO A SOURCE OF COMPRESSED GAS, A SHEATH OF HEAT INSULATING MATERIAL FITTING ROUND THE HEAT EX- 